The present invention relates to an improved ice thickness control system and associated sensor probe.
Ice-making machines are known in the art. They can take various forms, but share the general basic attribute that water is brought into contact with a cold element, such as an ice plate or coil, which is cooled to below the freezing point of water. The cold element may be submerged in a pool of water, or the water may be provided in a flow over the cold element. In either design, ice will begin to form on the surface of the cold element, growing in size over time. Eventually, when enough ice is formed, it is xe2x80x9charvested,xe2x80x9d so that it may be used as cubes, etc.
For example, U.S. Pat. No. 5,761,919 discloses an automatic ice-making machine including a water reservoir 10 and a cold plate 14 with a surface shaped so as to form ice cubes. A pump 12 pumps the water from the reservoir over the cold plate. The cold plate is maintained at a temperature below freezing so that a thickness of ice 16 forms on the cold plate. A capacitance-sensing circuit 20 is used to determine when the built-up ice should be harvested.
It will be appreciated that all ice-making machines need a system, preferably an automated system, for determining when the ice has built up sufficiently to be harvested. It is important to be able to consistently harvest the ice at the right time, when the mass of ice being harvested has the appropriate thickness such that the resulting ice cubes will meet required dimensional tolerances. For example, if the ice is allowed to become too thick before harvesting, the ice cubes will tend to bind to each other, making them hard to separate. Alternatively, if the ice is harvested while it is still too thin, the ice cubes will be undersized, which is undesirable from the end user""s perspective, as they will melt too quickly. Accordingly, there is a need in the art for an ice-making machine which can accurately determine when the ice should be harvested.
Typical prior art systems have used a variety of methods to detect the build-up of a sufficient amount of ice. Mechanical systems use micro-switches which are actuated when the ice surface contacts the switch. Such systems suffer from many drawbacks, including interference of ice with actuating parts, switch hysteresis, and tolerances.
Electrical resistance systems use metal a bridge sensor which conducts electricity when water is flowing over it. During the ice-making cycle, as the ice mass becomes thicker, it forces the flowing water to splash out further, eventually making continuous, or nearly continuous contact with the metal bridge, resulting in a substantially consistent signal in the associated circuit. This conductive signal is then interpreted by the system as an indication that the ice is thick enough to harvest. A serious drawback of this method is that water used in ice-making machines often contains impurities, which over time will coat a metal bridge sensor and stop it from conducting an electrical signal (the so-called xe2x80x9climing effectxe2x80x9d). When this happens, the sensor must be serviced or replaced. In locations where there is a relatively high level of water impurities, this coating with impurities (xe2x80x9climing upxe2x80x9d) may occur very quickly. Accordingly, there is a need in the art for an ice-making machine ice sensor which is less susceptible to the liming problem than known sensors.
It is also known to use thermal detection systems which use temperature sensors placed appropriately such that when the ice builds out to and contacts the sensor, a unique thermal signature is presented to the detector. However, the prior art thermal detection systems have a poor signal-to-noise ratio, which makes them unable to provide reproducible harvesting cycles.
Accordingly, there is a need in the art for an ice-making machine sensor which has no moving parts, does not suffer from liming problems, and which can accurately and reproducibly determine when the ice should be harvested.
Accordingly, the invention addresses this need by providing an improved ice thickness sensing and control system using an improved temperature sensor and control logic having several adjustable delay times to optimize performance.
It will be appreciated by one of ordinary skill in the art that the control logic, including that implementing the delay times, may be implemented in hardware, firmware, software, or any combination of thereof, as a matter of design choice. Accordingly, the term xe2x80x9ccircuitryxe2x80x9d as used herein means any combination of hardware, firmware, or software used to implement the control logic.
The invention is generally directed to an ice thickness control system which uses a temperature sensor mounted near the cold plate. As the ice thickens and gets closer to the sensor, the sensed temperature gets colder; finally when the ice is thick enough that it touches (or nearly touches) the sensor, the sensor will detect a very low temperature and will xe2x80x9cnotifyxe2x80x9d the control system to begin the harvesting process.
The invention is generally directed to a liquid-solidifying machine comprising a cold element, a liquid source, a temperature sensor, and circuitry associated with the sensor. The cold element includes a solid-forming surface which may be cooled to below the solidification point of the liquid. The liquid source provides liquid to the solid-forming surface such that a thickness of solid forms on the surface. The temperature sensor is provided with sufficient current that it self-heats to above the ambient temperature when the liquid-solidifying machine is in use. The circuitry associated with the sensor is operative to sense the temperature signal from the sensor, and detects when solid material formed on the cold surface is to be harvested.
In one embodiment, the liquid-solidifying machine is an ice-making machine; the liquid used in the system is water, and the solid is water ice. The temperature sensor in this embodiment self-heats sufficiently that no ice forms on the exterior surface of the sensor, preferably at least about 25xc2x0 F. above ambient temperature when the machine is in use, more preferably at least about 75xc2x0 F. above ambient temperature when the machine is in use. The temperature sensor is preferably a thermistor-type sensor, and may comprise a bead in a metal housing. The temperature signal from such sensors is not adversely affected by the deposition of impurities, from the liquid, on the exterior surface of the sensor. The temperature sensor may comprise a thermistor bead in a metal housing, the metal housing being mounted in a carrier, the position of the sensor relative to the solid-forming surface being adjustable.
The ice-making machine of the present invention comprises a cold element, a water source, a temperature sensor, and control logic associated with the sensor. The cold element includes an ice-forming surface which may be cooled to below the freezing point of water. The water source provides water to the ice-forming surface such that a thickness of ice forms on the surface during an ice-making cycle. The control logic detects when ice formed on the cold surface is to be harvested, and comprises a temperature signal threshold value, signal-sensing circuitry, threshold persistence circuitry, and harvesting cycle initiation circuitry. The temperature signal threshold value indicates when the thickness of ice is sufficiently close to the sensor such that it can be harvested. The signal-sensing circuitry is operative to sense the temperature signal from the sensor, the threshold persistence circuitry determines that the temperature signal has consistently remained above the threshold value for a threshold persistence time duration since the temperature signal first exceeded the threshold value. The harvesting cycle initiation circuitry initiates a harvesting cycle, during which the ice is removed from the ice-making surface.
The control logic may further comprise circuitry for determining that, starting from the beginning of the ice-making cycle, a minimum harvest time duration has elapsed, before the harvesting cycle can be initiated. It may also further comprise circuitry for determining that, starting from the end of the threshold persistence time duration, a harvesting delay time duration has elapsed, before a harvesting cycle can be initiated. The control logic may further comprise circuitry for determining that, starting from the end of the harvesting cycle, a recycling delay time duration has elapsed, before another ice-making cycle can be initiated.
A method of operating an ice-making machine is also provided, comprising the steps of: (a) providing a cold element; (b) providing a water source; (c) providing a temperature sensor; (d) providing circuitry associated with the sensor; (e) providing the circuitry with a temperature signal threshold value (which indicates when the thickness of ice is sufficiently close to the sensor such that it can be harvested); (f) initiating an ice-making cycle (during which the ice-making surface is cooled to below the freezing point of water, and water is provided to the ice-forming surface such that a thickness of ice forms on the surface); (g) a threshold persistence determination step, in which it is determined whether the temperature signal has consistently remained above the threshold value for a threshold persistence time duration since the temperature signal first exceeded the threshold value; and (h) a harvesting cycle initiation step, during which the ice is removed from the ice-making surface. The cold element includes an ice-forming surface which may be cooled to below the freezing point of water. The water source can provide water to the ice-forming surface. The circuitry associated with the sensor detects when ice formed on the cold surface is to be harvested, said circuitry being operative to sense the temperature signal from the sensor.
The steps (f) through (h) may be performed in alphabetical order, and may be repeated more than once. The method may include the further step of determining that, starting from the beginning of the ice-making cycle, a minimum harvest time duration has elapsed, before a harvesting cycle can be initiated. The method may also include the further step of determining that, starting from the end of the threshold persistence time duration, a harvesting delay time duration has elapsed, before a harvesting cycle can be initiated. The method may also include the further step of determining that, starting from the end of the harvesting cycle, a recycling delay time duration has elapsed, before another ice-making cycle can be initiated.